Hatches provide access to a generally sealed environment such as areas of a ship, tanker trailers, bunkers, and military vehicles. Such hatches must be constructed to meet the same structural requirements as the surrounding structure. Furthermore, the hatch must maintain the integrity of the sealed environment when locked down.
Traditional hatches open and close by pivoting along one edge of the hatch. Examples of conventional hatches are disclosed in U.S. Pat. No. 4,424,736 to Byrne; U.S. Pat. No. 6,293,051 to Matye; U.S. Pat. No. 5,137,327 to Edmonds et al.; and U.S. Pat. No. 5,220,127 to Tiomkin et al. The one-sided hinge has particular design advantages, but requires an unobstructed envelope for completing the hatch pivot. This becomes problematic when the barrel of a cannon or other object is in close proximity to the hatch. Therefore, there is a need for a hatch with a minimal opening envelope that does not interfere with other structures.
The structural requirements for a hatch frequently make them difficult to open. One of the main purposes of a tank hatch is to facilitate the movement of military personal, while providing the same level of protection as the rest of the tank structure. Depending upon the vehicle or embodiment, any particular hatch may include armor. Additional “top-attack” armor is commonly used to enhance protection when a vehicle is within a particularly high threat area. These survivability requirements drastically increase the weight of the hatch adding to the difficulty of operating the hatch.
Many traditional hinge assemblies utilized torsional springs to reduce the force required to open the side pivot hatch assemblies. Armor for the hatch of a tank, however, can be relatively heavy, and the torsion springs would have to be relatively large to be effective. Spring size would necessarily be further increased if top attack armor was used. However, large springs are bulky and impinge on the already limited interior working space. Furthermore, once the removable armor is taken off there is considerably less weight to the hatch, which in turn could create a potentially dangerous uncontrolled opening of the hatch due to the larger springs.
A hatch should be relatively easy to function, while remaining reliable. In a military vehicle, reliability must be maintained through rigorous and damaging conditional. The hatch of a military vehicle should accommodate the addition and removal of armor. The steps needed to open and close the hatch portal should be minimal, taking into consideration the amount of force and time needed to operate the hatch during emergencies. It would be desirable to have a hatch assembly in which the user can retain positive control over opening and closing. Further, opening the hatch should require as small an opening envelope as possible so as not to interfere with other operating features of the vehicle, such as a gun barrel or a military vehicle.